1. Technical Field
The present invention relates to laser padding materials and a laser padding method using the same and, more particularly, to a laser padding material and a laser padding method which contains copper as its major component and which is highly resistant to sliding abrasion and friction.
2. Background Art
Much attention is directed to laser padding (laser coating or laser cladding) techniques, because, in addition to the fact that the laser padding can finely control energy density (the diameter of a laser output beam), not only can it increase the processing speed and minimize the reduction of components in a padding alloy due to a parent or base material (that is, the reduction of the alloying components in their composition ratio resulting from the fact that the components of the base material are melted into the padding alloy and thus the alloy components are reduced in their composition ratio) but it can also apply a padded layer as thin as about 0.3 to 1.5 mm only to a necessary part of the base material.
Used as a laser padding apparatus which embodies the aforementioned laser padding, in such a laser padding apparatus as schematically shown in FIG. 3. With the apparatus, a laser beam 3 and such an inert gas as an argon (Ar) gas 4 or the like and padding metal powder 5 are supplied to a groove V provided in a surface of a base material 1 from a supply pipe 2 which is open to the groove V thereabove so that the powder 5 is rapidly melted on the base material 1 and then solidified, thereby forming a padded layer 6 on the base material.
When a laser beam is used, high speed processing can be achieved because the laser beam can provide much thermal energy to a desired local part of an object to be processed, whereby highly accurate padding dimensions can be realized. In addition, since the cooling rate can be high and fine crystalline grain can be obtained, the padded layer can be made high in quality and the processing yield can be also made high.
In this way, the laser padding method has a basic merit that padding can be effected so that the dimensions of the padded part are substantially equal to those of its desired finished product, thus providing a high material yield. And the laser padding method is conventionally used for such cobalt (Co) hardened metal as stellite or the like, nickel (Ni) hardened metal, and such iron (Fe) alloy as stainless steel or the like.
Conventional padding copper (Cu) materials include brass (Cu-Zn) alloy, phosphor bronze known as PBC2A, and copper-tin-lead (Cu-Sn-Pb) alloy known as LBC. It has been, however, impossible to use these materials in the laser padding method for the following reasons, thus disabling the laser padding using copper alloy.
(1) Brass (Cu-Zn) alloy
When a laser beam as a high-density energy source is used, the temperature of molten pool of such padding material exceeds a thousand and several hundred degrees of evaporates and thus padding is impossible, because the boiling point of zinc (Zn) is as low as 908.degree. C.
(2) PBC2A (Cu-Sn) alloy
This material tends to easily contain gas and thus cause some gas defects, though the material is one of copper alloys which can be used even under a high surface pressure and can be effectively used as sliding material.
(3) LBC (Cu-Sn-Pb) alloy
The laser padding provides a high-density energy as has been mentioned above, the processing rate is very fast, and the time period of such material necessary for its phase change from the solid state to the molten state after subjected to a laser beam irradiation, is as short as 0.1 to 0.5 seconds. As a result, the molten material is hardened or set before slag caused by the laser beam irradiation float up to the surface of the molten material, thus causing slag involvement within the padded part.
In addition, when it is desired to perform padding over a wide area by the laser padding method, linear padded layers must be overlapped by each other as shifted mutually slightly as shown in FIG. 4, which results in that slag formed on the surface of the previous padded layer is involved within the next padded layer during the next padding operation, as shown in FIG. 5.
In this manner, since any copper alloys have not been able to be employed in the laser padding method, the realization of copper laser padding material excellent in its sliding-abrasion resistant characteristic has been desired.
In view of the aforementioned circumstances in the prior art, it is an object of the present invention to provide a laser padding material (based on copper) and a laser padding method using the same which is highly resistant to sliding abrasion and friction and which allows a high quality of laser padding.